It is known to make use of electronic control circuits for controlling the power supply for energising the winding of the contactor. Such electronic circuits give substantially perfect control of the displacement of the movable core of the contactor, this displacement being that which, firstly, puts the starter pinion into mesh with the toothed starter crown of the internal combustion engine of a motor vehicle, and secondly completes the power circuit so as to start the electric starter motor which initially drives the vehicle engine in rotation.
It was originally proposed to arrange the electronic circuit on the outside of the contactor, but it rapidly became clear that it was preferable to incorporate it with the front cover of the contactor, so as to reduce the total bulk of the latter. However, electronic circuits are very sensitive to dust, humidity and the presence of metallic particles that can cause unwanted electrical contacts to occur between the different electrical connections of the circuit.
In contactors according to the present state of the art, the electronic circuit, in the form of a printed circuit board, is arranged within a compartment in the cover, this compartment being bounded on the rear by a separating wall or partition. However, this compartment is not sealed, due to the fact that the plunger which actuates displacements of the contact plate passes axially and centrally through this compartment. As a result, given that the control plunger must slide axially through two axial holes, formed in the fixed magnetic core and in the separating partition, it is necessary to provide a radial clearance between the plunger and these holes. Thus, during axial displacements of the control plunger, dusts or humidity are able to enter the compartment in which the electronic circuit is mounted.